1. Field of the Invention
The present invention relates to driving circuits, and particularly to a driving circuit having current balancing functionality.
2. Description of the Prior Art
FIG. 1 is a diagram of a light-emitting diode (LED) driving circuit. As shown in FIG. 1, when LED driving circuit 100 operates, front-end current setting unit 110 generates setting current Ipset according to reference voltage, current mirror 120 outputs bias current Ib according to setting current Ipset, bias resistor Rb provides bias voltage Vb according to bias current Ib, and a plurality of current driving modules 130 provide a plurality of driving currents Idr_1-Idr_N according to bias voltage Vb to drive a plurality of LED units 190 to emit output light having preset brightness. Current driving modules 130 described above utilize operational amplifier OP in coordination with feedback voltage provided by current-limit resistor Rc to perform error amplification processing, thereby driving buffer Buf to output driving voltage for controlling operation of transistor Qc.
However, offset voltage of each operational amplifier OP is not the same, so the current driving modules 130 have a hard time providing relatively similar driving currents Idr_1-Idr_N to drive the plurality of LED units 190 to generate uniform output light. Additionally, the lower bias voltage Vb is, the higher output voltage error percentage of operational amplifier OP is, i.e. output voltage error percentage of each operational amplifier OP changes with bias voltage Vb. Thus, LED driving circuit 100 not only has a hard time driving the plurality of LED units 190 to generate uniform output brightness, but also has a hard time performing precise control of driving currents over large ranges.